Predicting capacity of hard carbon anodes in sodium-ion batteries using porosity measurements

Is single layer graphene a promising anode for sodium-ion batteries?

“…All these experiments were performed using 1M NaPF 6 (EC:DEC, 1:1, w:w) as the electrolyte solution. In general terms, the intense cathodic and anodic peaks due to the insertion and de-insertion processes of Na + ions in carbon materials [5,7,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] do not appear in the CVs of SLG/Cu electrodes. More specifically, the CV of cycle 1 displays a significant cathodic current that has been previously observed in the study of the interaction of Li + ions with SLG [34] and attributed to the formation of a solid electrolyte interphase (SEI) layer as a consequence of the electrolyte irreversible reduction.…”

“…3, the cells start to show good electrochemical performance in terms of cycling stability as well as coulombic efficiency (≥ 90 %, ≥ 85 % for NaClO 4 in PC electrolyte) after 20 discharge-charge cycles. However, during the initial cycles (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), these electrochemical parameters, particularly the capacity retention, were much lower.…”

“…Therefore, efforts have been focused on the identification of other host carbon materials to achieve a successful reversible intercalation/insertion of the larger Na + anions. Thus, a variety of carbons having a certain degree of porosity, a low-ordered structure consisting of few-layers graphite nanocrystallites (graphite domains) and different morphologies, including hard and soft carbons [5,7,[11][12][13][14][15], carbon fibers and nanofibers [16][17][18][19][20], spherical carbons [21], hollow carbon nanowires [22] and nanospheres [23], reduced graphene oxide, [24] pyrolytic carbons from graphite oxide [25], as well as highly disordered carbon composites [26,27] have been investigated as anodes for SIBs. Good results as regards capacity and cycling stability were achieved with some of these carbons, the rate capability and particularly, the low coulombic efficiency during the first charge/discharge cycle due to the relatively large surface area (as compared with graphitic carbons) being the main drawbacks to overcome.…”

“…Good results as regards capacity and cycling stability were achieved with some of these carbons, the rate capability and particularly, the low coulombic efficiency during the first charge/discharge cycle due to the relatively large surface area (as compared with graphitic carbons) being the main drawbacks to overcome. In these porous disordered carbons, the electrochemical storage of Na + ions occurs through two predominant mechanisms, insertion between the graphene layers of the small graphitic clusters in the higher potential region ( 1.5-0.1 V vs Na/Na + ) resulting in a sloping voltage profile, and/or adsorption by filling the porous structure as showed by the plateau at the lowest potentials (< 0.1 V vs Na/Na + ) [7,11,19,23].…”

“…capacity and cycling stability were achieved with some of these carbons, the rate 4 capability and particularly, the low coulombic efficiency during the first charge/discharge cycle due to the relatively large surface area (as compared with graphitic carbons) being the main drawbacks to overcome. In these porous disordered carbons, the electrochemical storage of Na + ions occurs through two predominant mechanisms, insertion between the graphene layers of the small graphitic clusters in the higher potential region ( 1.5-0.1 V vs Na/Na + ) resulting in a sloping voltage profile, and/or adsorption by filling the porous structure as showed by the plateau at the lowest potentials (< 0.1 V vs Na/Na + ) [7,11,19,23].Thus, no voltage plateaux were observed in the electrochemical profiles of electrospun carbon nanofibers [19] and reduced graphene oxide [24], indicating that the capacity was mainly due to the sodium insertion into the graphene layers.A common feature for these carbons is the large interlayer spacing [19,23,24], all of them having values  0.37 nm, which has been determined from theoretical calculations to be the critical minimum value required to allow good reversible Na + ion insertion [22]. On the contrary, a large proportion of the capacity provided by other carbons was ascribed to the adsorption of sodium into the pores [7].…”